The Astrocalculator

The KStars Astrocalculator provides several modules that give you direct access to algorithms used by the program. The modules are organized by subject:

Coordinate Converters

Earth Coordinates

Time Calculators

Apparent Coordinates module


Apparent Coordinates

The Apparent Coordinates module converts the catalog coordinates of a point in the sky to its apparent coordinates for any date. The coordinates of objects in the sky are not fixed, because of precession, nutation and aberration. This module takes these effects into account.

To use the module, first enter the desired target date and time in the Target Time/Date section. Then, enter the catalog coordinates in the Catalog Coordinates section. You can also specify the catalog's epoch here (usually 2000.0 for modern object catalogs). Finally, press the Compute button, and the object's coordinates for the target date will be displayed in the Apparent Coordinates section.

Equatorial/Galactic Coordinates module


Equatorial/Galactic Coordinates

This module converts from Equatorial coordinates to Galactic coordinates, and vice versa. First, select which coordinates should be taken as input values in the Input Selection section. Then, fill in the corresponding coordinate values in either the Galactic coordinates or Equatorial coordinates section. Finally, press the Compute button, and the complementary coordinates will be filled in.

Horizontal Coordinates module


Horizontal Coordinates

This module converts from Equatorial coordinates to Horizontal coordinates. First, select the date, time, and geographic coordinates for the calculation in the Input Data section. Then, fill in the equatorial coordinates to be converted and their catalog epoch in the Equatorial Coordinates section. When you press the Compute button, the corresponding Horizontal coordinates will be presented in the Horizontal Coordinates section.

Precession module


Precession

This module is similar to the Apparent Coordinates module, but it only applies the effect of precession, not of nutation or aberration.

To use the module, first enter the input coordinates and their epoch in the Original Coordinates section. You must also fill in the target epoch in the Precessed Coordinates section. Then, press the Compute button, and the object's coordinates, precessed to the target Epoch are presented in the Precessed Coordinates section.

Geodetic Coordinates module


Geodetic Coordinates

The normal geographic coordinate system assumes that the Earth is a perfect sphere. This is nearly true, so for most purposes geographic coordinates are fine. If very high precision is required, then we must take the true shape of the Earth into account. The Earth is an ellipsoid; the distance around the equator is about 0.3% longer than a Great Circle that passes through the poles. The Geodetic Coordinate system takes this ellipsoidal shape into account, and expresses the position on the Earth's surface in cartesian coordinates (X, Y, and Z).

To use the module, first select which coordinates you will use as input in the Input Selection section. Then, fill in the input coordinates in either the Cartesian Coordinates section or the Geographic Coordinates section. When you press the Compute button, the corresponding coordinates will be filled in.

Day Duration module


Day Duration

This module computes the length of day as well as sunrise, sun-transit (noon), and sunset times for any calendar date, for any location on Earth. First fill in the desired geographic coordinates and date, then press the Compute button.

Julian Day module


Julian Day

This module converts between the calendar date, the Julian Day, and the Modified Julian Day. The Modified Julian Day is simply equal to the Julian Day - 2,400,000.5.

To use the module, select which of the three dates will be the input, and then fill in its value. Then press the Compute button, and the corresponding values for the other two date systems will be displayed.

Tip

Exercise:

What calendar date does MJD = 0.0 correspond to?

Sidereal Time module


Sidereal Time

This module converts between Universal Time and Local Sidereal Time. First, select whether you will use Universal Time or Sidereal Time as an input value in the Input Selection section. You must also specify a geographic longitude, and a date for the calculation, in addition to either the Universal Time or the Sidereal Time value. When you press the Compute button, the corresponding value for the other Time will be displayed.